Binary alloy single-crystalline metal nanostructures and fabrication method thereof

ABSTRACT

Disclosed are a method of fabricating a binary alloy nanostructure by using metal oxides, metal substances or metal halides of metal elements used to form a binary alloy and/or binary alloy substances as a precursor through a vapor phase synthesis method and a binary alloy nanostructure fabricated by the same. More particularly, the present invention provides a method of fabricating a binary alloy nanowire or nanobelt which comprises placing a precursor on the front part of a reaction furnace and a substrate on the rear part of the furnace, and heat treating both of them under inert gas atmosphere to produce the nanowire or nanobelt and, in addition, a binary alloy nanowire or nanobelt fabricated by the method according to the present invention.

This application claims priority to Korean Patent Application No. 2007-0068548, filed on Jul. 9, 2007, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to binary alloy single-crystalline metal nanostructures and a fabrication method thereof, and more particularly, to a binary alloy single-crystalline nanostructure and a method for fabrication thereof by vapor phase synthesis.

2. Description of the Related Art

In recent years, one dimensional (1D) nanostructures often represented by nanowires have been drawing extensive attention as a material highly applicable, especially, in semiconductor applications. Such nanostructures are expected to have various advantages including decreased size, increased aspect ratio, increased surface to volume ratio and, newly discovered phenomena and unique characteristics owing to novel morphologies thereof, which cannot be observed in bulk states.

In particular, there is a great deal of interest for binary alloy nanowires useable in manufacturing gas sensors, magnetic devices and/or magnetic sensors. There is an important requirement for developing a variety of precision measurement sensors useful for high precision works following recent advances in science and technologies. Also, development of improved sensors with excellent sensitivity by domestic and/or oversea research activities is still a long way off.

Moreover, with regard to hydrogen gas sensors for highly sensitive fuel cells that can detect hydrogen leaks that may occur, if such fuel cells are to become commercially available on the market, there is still a requirement that such sensors require much more research and development together with novel fuel cells to be used as a future clean energy.

In addition to the development of hydrogen sensors described above, it is also important to investigate novel materials useable in manufacturing the sensors. Among them, a PdAu nanowire is receiving much attention, which comprises PdAu having strong adhesiveness to hydrogen and can be applied to high precision sensors. Since the PdAu nanowire shows no phase transition from α to β at a defined hydrogen concentration ranging from 0.1 to 2%, it is expected that this can improve a response time of a hydrogen sensor if used in the sensor.

A CoAg alloy nanowire has magnetic properties such as magnetic resistance MR, spin glass properties, etc., while an AgTe alloy nanowire typically shows combined ionic and charge conductive properties. When it. In a circumstance with high temperature, AgTe substances include one having superionic conductivity and a high content of Ag in a bulk condition and another having large positive MR properties and a high content of Te. Therefore, both of the CoAg alloy nanowire and the AgTe alloy nanowire are also expected to be practically utilized in manufacturing nano-sized magnetic sensors or magnetic devices.

However, it is known that CoAg alloy has positive combined energy in a binary system of Co and Ag and it is difficult to generate an intermetallic compound thereof. Thus, papers for reviewing CoAg alloy were not disclosed before the 1990s. The reported substances comprise kinds of thin films and nano particles in amorphous and/or multi-crystalline forms.

Like CoAg alloy nanowires, no reports have yet disclosed the fabrication of nanocables or single-crystalline metal nanowires based on PdAu and/or AgTe alloys. There is still no disclosure that introduces application of vapor phase synthesis in production of binary alloy nanowires under catalyst free circumstances.

At present, it is difficult to produce nanocables using binary metals and, even more, using single metals. Most of recently disclosed documents have a focus on synthesis of nano-sized structures using bulk metals. For synthesis of 1D nanostructures, most of research groups make use of an anodic aluminum oxide template as the most simple method. This method is most convenient in synthesizing 1D nanostructures and is receiving increased interest in an aspect of diameter control that can regulate the diameter of a nanocable dependent on conditions for synthesis, however, it has difficulty in synthesis of single-crystalline metal nanowires.

Synthesis of single-crystalline metal nanowires is a significant element in view of improved electric and magnetic properties of raw substances. The most important factor related to electric properties of a nanowire is a degree of electron conductivity. For a single-crystalline metal nanowire, the nanowire itself is a large grain boundary and has no obstacles against electron conductivity in the nanowire.

On the other hand, a multi-crystalline metal nanowire which comprises a number of grains and grain boundaries exhibits a decrease in the electron conductivity due to electron scattering caused by a number of boundary barriers.

For magnetic properties of a nanowire, an arrangement of electron spin is substantially important when applying an external field to the nanowire. As described above, the single-crystalline metal nanowire has only a single crystal form to orient the arrangement of electron spin in a single direction if the external field is applied. While, the multi-crystalline metal nanowire as a set of numerous crystals induces the crystals to arrange electron spins in different directions during application of the external field, thus resulting in reduction of magnetic properties thereof.

In order to solve the above problems, the present inventors intended to apply vapor phase synthesis of binary alloy nanostructures using metal oxides, metal substances, metal halides and/or binary alloy materials as a precursor and, as a result, completed a process for production of a binary alloy single-crystalline nanostructure with a completed morphology.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to solve problems of prior art as described above and, an object of the present invention is to provide a binary alloy single-crystalline nanostructure with high quality and improved morphology, and a method for fabrication of the same through a vapor phase transport method.

In order to accomplish the above object, the present invention provides a method of fabricating a binary alloy single-crystalline nanostructure, comprising: using two substances selected from a first material to a third material separately or in a combination thereof as a precursor; and heat treating the precursor as well as a semiconductor or insulator single-crystalline substrate under inert atmosphere after placing the precursor on front part of a reaction furnace and the single-crystalline substrate on rear part of the reaction furnace to fabricate a binary alloy single-crystalline metal nanowire or nanobelt, wherein the binary alloy for the nanostructure includes the first material containing metal oxides, metal substances or metal halides of a metal used to form the binary alloy, a second material containing metal oxides, metal substances or metal halides of another metal used to form the binary alloy, and/or the third material containing any one of binary alloy substances for the binary alloy.

According to the present invention, the precursor includes a mixture of the first material and the second material, a mixture of the first material and the third material, or the third material alone.

Preferably, metal halides of the first material or the second material are selected from a group consisting of metal fluoride, metal chloride, metal bromide and metal iodide.

In case that the single-crystalline nanostructure according to the present invention is a single-crystalline metal nanowire, an inert gas flow is introduced through the front part to the rear part of the furnace at 10 to 600 sccm, the heat treatment is conducted under pressure ranging from 2 to 30 torr, and the precursor is maintained at 500 to 1200° C. while the single-crystalline substrate is maintained at 700 to 1100° C.

In case that the single-crystalline nanostructure according to the present invention is a single-crystalline metal nanobelt, an inert gas flow is introduced through the front part to the rear part of the furnace at 10 to 600 sccm, the heat treatment is conducted under pressure ranging from 2 to 30 torr, and the precursor is maintained at 500 to 1200° C. while the single-crystalline substrate is maintained at 100 to 200° C.

In a case that metal halides are used as the precursor, that is, the precursor is a mixture containing metal halides of the first material as well as the second material, it is preferable that metal halides of the first material and the second material are physically separate from each other and positioned at the front part of the reaction furnace.

At this time, metal halides of the first material are maintained at 500 to 800° C. and the second material is maintained at 800 to 1200° C., while the single-crystalline substrate is maintained at 700 to 1100° C.

Preferably, metal oxides of the first material or the second material are selected from a group consisting of silver oxide, gold oxide, cobalt oxide, palladium oxide and tellurium oxide. Preferably, metal substances of the first material or the second material are selected from a group consisting of silver, gold, cobalt, palladium and tellurium in terms of metal element. Preferably, metal halides of the first material or the second material are selected from a group consisting of silver halide, gold halide, cobalt halide, palladium halide and tellurium halide. Preferably, binary alloy substances of the third material include Co and Ag alloy, Ag and Te alloy, or Bi and Te alloy.

Preferably, the binary alloy single-crystalline metal nanowire formed on the single-crystalline substrate is selected from a Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire, a Co_(y)Ag_(1-y) (0.01≦y≦0.5) single-crystalline metal nanowire, a Ag₂Te nanowire and a Bi₁Te₁ single-crystalline metal nanobelt.

According to the present invention, there is provided a binary alloy nanostructure comprising a solid solution of single crystals of two metal elements or a compound of the single crystals, in which the metal elements are selected from metals or metalloids, wherein the structure is fabricated by using a precursor under a catalyst through a vapor phase synthesis method.

At this time, the precursor includes two substances selected from a first material to a third material separately or in a combination thereof, and the binary alloy for the nanostructure includes the first material containing metal oxides, metal substances or metal halides of a metal used to form the binary alloy, a second material containing metal oxides, metal substances or metal halides of another metal used to form the binary alloy, and/or the third material containing any one of binary alloy substances for the binary alloy.

In case that the single-crystalline nanostructure according to the present invention is a single-crystalline metal nanowire, the precursor is maintained at 500 to 1200° C. while a substrate for fabrication of a binary alloy single-crystalline metal nanowire is maintained at 700 to 1100° C., and an inert gas flow is introduced from the precursor to the substrate at 10 to 600 sccm under pressure ranging from 2 to 30 torr to prepare the nanowire.

In case that the single-crystalline nanostructure according to the present invention is a single-crystalline metal nanobelt, the precursor is maintained at 500 to 1200° C. while a substrate for fabrication of a binary alloy single-crystalline metal nanobelt is maintained at 100 to 200° C., and an inert gas flow is introduced from the precursor to the substrate at 10 to 600 sccm under pressure ranging from 2 to 30 torr to prepare the nanobelt.

Preferably, the binary alloy nanowire is selected from a Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire, a Co_(y)Ag_(1-y) (0.01≦x≦0.5) single-crystalline metal nanowire, a Ag₂Te nanowire and a Bi₁Te₁ single-crystalline metal nanobelt.

Preferably, the Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire has a FCC (Face Centered Cubic) structure. Preferably, the Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire is in the form of a solid solution. Preferably, the Co_(y)Ag_(1-y) (0.01≦x≦0.5) single-crystalline metal nanowire has a FCC (Face Centered Cubic) structure. Preferably, the Co_(y)Ag_(1-y) (0.01≦x≦0.5) single-crystalline metal nanowire is in the form of a solid solution.

Preferably, the Ag₂Te single-crystalline metal nanowire has an SM (Simple Monoclinic) structure. Preferably, the Ag₂Te single-crystalline metal nanowire is in the form of a compound. Preferably, the Bi₁Te₁ single-crystalline metal nanobelt has a hexagonal structure.

The present inventive method adopts a vapor phase transport method without a catalyst to fabricate a binary alloy metal nanowire, thus improving simplicity and reproducibility in working processes for fabrication of the nanowire. This method also has advantages in that the fabricated nanowire is a high quality nanowire or nanobelt in a complete single-crystalline condition without defects and the binary alloy nanowire or nanobelt can be massively produced in a uniform size without coagulation on a single-crystalline substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, aspects, and advantages of the present invention will be more fully described in the following detailed description of preferred embodiments and examples, taken in conjunction with the accompanying drawings. In the drawings:

FIG. 1 is a diagram illustrating heat treatment of a precursor and a substrate described in Example 2 of the present invention;

FIG. 2 is a SEM (Scanning Electron Microscope) photograph of a nanowire fabricated as described in Example 1 of the present invention;

FIG. 3 is an XRD (X-Ray Diffraction) photograph of a nanowire fabricated as described in Example 1 of the present invention;

FIG. 4 shows a result monitored by EDS (Energy Dispersive Spectroscopy) fixed to a TEM (Transmission Electron Microscope) device for analysis of a nanowire fabricated as described in Example 1 of the present invention;

FIG. 5 shows TEM analysis results for a nanowire fabricated as described in Example 1 of the present invention, in particular, FIG. 5( a) illustrates a dark field image; FIG. 5( b) is a high magnitude TEM photograph of the nanowire shown in FIG. 5( a); and FIG. 5( c) illustrates a SAED (Selected Area Electron Diffraction) pattern of the nanowire shown in FIG. 5( a);

FIG. 6 is a SEM photograph of a nanowire fabricated as described in Example 2 of the present invention;

FIG. 7 is an XRD photograph of a nanowire fabricated as described in Example 2 of the present invention;

FIG. 8 illustrates a dark field image of a nanowire fabricated as described in Example 2 of the present invention, in particular, a SAED pattern of the nanowire being inserted in a lower left part thereof;

FIG. 9 shows results monitored by EDS fixed to a TEM device for analysis of constitutional ingredients of a nanowire fabricated as described in Example 2 of the present invention, in particular, FIG. 9( a) is an Ag EDS mapping result of the nanowire; FIG. 9( b) is a Co EDS mapping result of the nanowire; FIG. 9( c) is an EDS result of a white blank square portion indicated on an upper part of the nanowire; and FIG. 9( d) is an EDS result of another white blank square portion indicated on a lower part of the nanowire;

FIG. 10 is a SEM photograph of a nanowire fabricated as described in Example 3 of the present invention;

FIG. 11 is an XRD result of a nanowire fabricated as described in Example 3 of the present invention;

FIG. 12 shows TEM analysis results of a nanowire fabricated as described in Example 3 of the present invention, in particular, FIG. 12( a) illustrates a dark field image and SAED pattern of the nanowire; FIG. 12( b) is a HRTEM (High Resolution Transmission Microscopy) photograph of the nanowire shown in FIG. 12( a) and, in addition, FFT (Fast Fourier Transform) pattern inserted in an upper right part thereof;

FIG. 13 shows a result monitored by EDS fixed to a TEM device for analysis of a nanowire fabricated as described in Example 3 of the present invention;

FIG. 14 shows TEM analysis results of a Bi₁Te₁ nanobelt, in particular, FIG. 14( a) illustrates a dark field image and SAED pattern of the nanobelt and FIG. 14( b) is a HRTEM photograph of the nanobelt together with FFT pattern inserted in an upper right part thereof;

FIG. 15 shows a result monitored by EDS fixed to a TEM device for analysis of constitutional ingredients of a nanobelt fabricated as described in Example 4 of the present invention; and

FIG. 16 shows an XRD result of a nanobelt fabricated as described in Example 4 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in more detail by the following examples with reference to the accompanying drawings.

The a method of fabricating a binary alloy single-crystalline nanostructure of the present invention comprises using two substances selected from a first, a second and a third material separately or in a combination thereof as a precursor; and heat treating the precursor as well as a semiconductor or insulator single-crystalline substrate under inert atmosphere after placing the precursor on front part of a reaction furnace and the single-crystalline substrate on rear part of the reaction furnace to fabricate a binary alloy single-crystalline metal nanowire or nanobelt. In the present invention, the binary alloy for the nanostructure includes the first material containing metal oxides, metal substances or metal halides of a metal used to form the binary alloy, the second material containing metal oxides, metal substances or metal halides of another metal used to form the binary alloy, and/or the third material containing any one of binary alloy substances for the binary alloy.

The method of fabricating a binary alloy nanowire or a nanobelt according to the present invention is characterized by simply using a precursor, which is any one selected from binary alloy materials and metal oxides, metal substances or -metal halides of two metals used to form a binary alloy so as to fabricate the nanowire or nanobelt on a substrate. The present inventive method has improved simplicity and reproducibility in fabrication processing because a binary alloy single-crystalline metal nanowire or nanobelt can be fabricated without a catalyst through a vapor phase transport path and, in addition, an advantage of fabricating high purity nanostructures without impurities other than the two metals used to form the binary alloy.

By regulating temperatures of front and rear parts of a reaction furnace, respectively, and inert gas flow rate and internal pressure of a heat treatment pipe during heat treatment, this method ultimately controls nucleation driving power, growth driving power, nucleation velocity and growth velocity so as to control and reproduce size of the binary alloy single-crystalline nanostructure and density of a substrate and further produce high quality and good crystallinity binary alloy single-crystalline nanostructures without defects.

A heat treatment condition, carrier gas (that is, inert gas) flow rate and a pressure condition in heat treatment can be independently adjustable. But, in order to obtain a binary alloy single-crystalline metal nanowire with preferable quality and morphology, it is desirable that all of these conditions are altered dependent on other conditions. Therefore, specific defined limits for these conditions have substantially no meanings independently, however, a combination thereof can induce the most preferable product, that is, the binary alloy single-crystalline metal nanowire.

Temperatures of the front and the rear parts of the reaction furnace, respectively, must be optimally defined depending on physical properties of the precursor such as melting point, vaporization point, vaporization energy, etc. and conditions for carrier gas flow rate and pressure in heat treatment. Preferably, the precursor is maintained at 500 to 1200° C. while a substrate is maintained at 700 to 1100° C. for a nanowire and at 100 to 200° C. for a nanobelt.

The carrier gas, that is, an inert gas preferably flows from the front part of the reaction furnace toward the rear part of the same in an amount of 10 to 600 sccm. If the precursor includes metal halides, the inert gas preferably flows from the front part to the rear part of the furnace in an amount of 300 to 600 sccm and, more preferably, 450 to 550 sccm. When the precursor does not include metal halides, the inert gas preferably flows from the front part to the rear part of the reaction furnace in an amount of 10 to 300 sccm. The pressure in heat treatment is preferably lower than ordinary pressure, more preferably, ranges from 2 to 30 torr and, most preferably, from 5 to 15 torr. However, in case of the precursor comprising metal halides, there is no problem to apply the ordinary temperature to fabrication of the nanowire.

Conditions such as temperature of a reaction furnace, inert gas flow rate and pressure in heat treatment may influence various parameters including: degree of gasification of a precursor; amount of the precursor gasified and transferred per hour to a single-crystalline substrate; nucleation and growth velocities of a binary alloy material on the single-crystalline substrate; and surface energy, degree of coagulation, and/or morphology of a binary alloy material (such as nanowire or nanobelt) produced on a single-crystalline substrate.

Accordingly, under such conditions in relation to the temperature, the inert gas flow rate and the pressure in heat treatment, a binary alloy nanowire or nanobelt with the most preferable quality and morphology is produced by a vapor phase transport method, using the precursor according to the present invention. Beyond the defined ranges for the conditions described above, it is difficult to fabricate a binary alloy based nanowire and, even when a nanowire or nanobelt is produced, there may occur some problems such as coagulation of the product, modified morphologies, poor quality caused by defects or failure, or that other metal materials in forms of a particle, rod, etc. are generated instead of a preferable nanowire or nanobelt morphology.

Heat treatment time should also be optimally defined under the conditions described above including temperature, inert gas flow rate and the pressure in heat treatment, and preferably, ranges from 10 minutes to 1 hour. During the heat treatment time defined above, the precursor gasified by the inert gas migrates to a single-crystalline substrate to participate in nucleation and nuclei growth and, simultaneously, a material transfer (in atomic or cluster unit) occurs between binary alloy substances generated on the substrate through a vapor phase and a surface of the substrate, thus resulting in Oswald ripening.

Accordingly, the single-crystalline substrate on which the binary alloy nanowire or nanobelt was formed after the heat treatment, is again subjected to the heat treatment so as to regulate density or size of the nanowire or nanobelt or the like.

As described above, the fabrication method of the present invention uses metal oxides, metal substances or metal halides of two metal elements for fabricating a binary alloy metal nanowire or nanobelt, otherwise, binary alloy materials of the above two metal elements, as a precursor and adopts the vapor phase transport method to produce the binary alloy nanowire or nanobelt. The binary alloy single-crystalline metal nanowire or nanobelt formed on the single-crystalline substrate preferably comprises Pd_(x)Au_(1-x) (x is 0.01≦x≦0.99) single-crystalline metal nanowire, Co_(y)Ag_(1-y) (y is 0.01≦y≦0.5) single-crystalline metal nanowire, Ag₂Te single-crystalline metal nanowire or Bi₁Te₁ single-crystalline metal nanobelt and so on.

The precursor for fabricating the binary alloy single-crystalline metal nanowire or nanobelt may include a mixture or two separate materials containing two metal elements used to fabricate a binary alloy.

In case of using a mixture as the precursor, the mixture may be a mixture of the first material and the second material or another mixture of the first material and the third material. Alternatively, the precursor may comprise an alloy of the two metal elements (which is substantially the third material) for fabricating a binary alloy metal nanowire or nanobelt alone. The mixture of the first and second materials includes, for example: a mixture containing metal oxides of the first material and metal oxides of the second material; a mixture containing metal substances of the first material and metal oxides of the second material; a mixture containing metal halides of the first material and metal oxides of the second material; a mixture containing metal oxide of the first material and metal substances of the second material; a mixture containing metal substances of the first material and metal substances of the second material; a mixture containing metal halides of the first material and metal substances of the second material; a mixture containing metal oxides of the first material and metal halides of the second material; a mixture containing metal substances of the first material and metal halides of the second material; or a mixture containing metal halides of the first material and metal halides of the second material. The mixture preferably comprises a mixture containing metal oxides of the first material and metal oxides of the second material, a mixture containing metal substances of the first material and metal oxides of the second material; a mixture containing metal oxides of the first material and metal substances of the second material; or a mixture containing metal substances of the first material and metal substances of the second material.

The mixture of the first and third materials includes, for example: a mixture containing metal oxides of the first material and binary alloy substances of the third material; a mixture containing metal substances of the first material and binary alloy substances of the third material; or a mixture containing metal halides of the first material and binary alloy substances of the third material. Metal oxides of the first material and binary alloy substances of the third material or metal substances of the first material and binary alloy substances of the third material are preferably used.

As the precursor, binary alloy substances of the third material may be used alone.

The mixture is not a simple mixture of the first material and the second material but means that two materials are positioned adjacent to each other in the reaction furnace (at a position maintaining the same temperature).

In particular, when using metal halides as the precursor, metal halides of the first material are used together with the second material and both of the materials are physically separate from each other and preferably positioned at front part of the reaction furnace. In order that the metal halides of the first material are physically separate from the second material and both materials are positioned on the front part of the reaction furnace, the second material and the metal halides of the first material are placed in difference pots and maintained at different temperatures, respectively, to participate in synthesis of a nanowire or nanobelt. Metal halides have relatively high volatility compared to metals, binary metals and metal oxides, and thus there is a need to control an amount of metal halide gas flowing to a substrate according to the inert gas flow rate.

Herein, the precursor includes a mixture containing metal halides of the first material and metal oxides of the second material, a mixture containing metal halides of the first material and metal substances of the second material, or a mixture containing metal halides of the first material and metal halides of the second material. Preferably, the precursor includes a mixture containing metal halides of the first material and metal oxides of the second material or a mixture containing metal halides of the first material and metal substances of the second material.

Alternatively, the precursor may include a mixture containing metal halides of the first material and binary alloy substances of the third material. Metal halides of the first material as well as the second material (or the third material) are physically separate from each other and placed on the front part of the reaction furnace. Temperature of metal halides of the first material ranges from 500 to 800° C., while temperature of the second material (or the third material) ranges from 800 to 1200° C. The substrate is preferably maintained at 700 to 1100° C. for a nanowire and 100 to 200° C. for a nanobelt, respectively.

If the reaction furnace has a single thermostat, the precursor is placed in a uniform zone of a reactor pipe and other materials or the substrate is located at another position defined by adjusting a distance between the precursor and the uniform zone in order to control temperature. In case that a heating element as well as the thermostat are installed independent of the reaction furnace, temperature of the reaction furnace can be controlled by operation of the thermostat.

Metal halides of the first material or the second material are selected from a group consisting of metal fluoride, metal chloride, metal bromide and metal iodide and, preferably, include silver halide, gold halide, cobalt halide, palladium halide or tellurium halide. Silver halide is preferably selected from a group consisting of silver fluoride, silver chloride, silver bromide and silver iodide. Likewise, gold halide is selected from a group consisting of gold halide, gold chloride, gold bromide and gold iodide; cobalt halide is selected from cobalt fluoride, cobalt chloride, cobalt bromide and cobalt iodide; palladium halide is selected from a group consisting of palladium fluoride, palladium chloride, palladium bromide and palladium iodide; and tellurium halide is selected from a group consisting of tellurium fluoride, tellurium chloride, tellurium bromide and tellurium iodide.

Metal oxides of the first material or the second material are preferably selected from a group consisting of silver oxide, gold oxide, cobalt oxide, palladium oxide and tellurium oxide. Herein, gold oxide, cobalt oxide, palladium oxide or tellurium oxide may be an oxide having a desired stoichiometric ratio with thermodynamic stability at ordinary temperature under ordinary pressure. However, such oxide may not have a stable stoichiometric ratio due to point defects caused by metal ingredients or oxygen.

Metal substances of the first material or the second material are preferably silver, gold, cobalt, palladium or tellurium.

Binary alloy substances of the third material are preferably selected from a group consisting of: Pd and Au (PdAu) alloy; Co and Ag (CoAg) alloy; Ag and Te (AgTe) alloy; and Bi and Te (BiTe) alloy. PdAu alloy, CoAg alloy or AgTe alloy may take the form of an inter-metallic compound, compound or solid solution. Constitutional composition of the alloy is preferably similar to that of a nanowire or nanobelt to be fabricated, although the composition may be different from that of the nanowire or nanobelt.

Meanwhile, a semiconductor or a non-conductor single-crystalline substrate is made of any one of semiconductors or non-conductors, which are chemically or thermally stable under certain heat treatment conditions described above. The substrate preferably includes any one selected form a single-crystalline substrate based on a group IV element such as silicon, germanium or silicon germanium; a single-crystalline substrate based on group III-V elements such as gallium-arsenic, indium-phosphorous or gallium-phosphorous; a single-crystalline substrate based on group II-VI elements; a single-crystalline substrate based on group IV-VI elements; a sapphire single-crystalline substrate; or a silicon dioxide single-crystalline substrate.

However, the substrate only plays a role of providing a space on which a nanowire or nanobelt is formed and, if necessary, may be a poly-crystalline substance of a substance included the single-crystalline substrate made of any one selected from the materials described above.

In order to experimentally identify improvements of the present inventive fabrication method, a Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire, a Co_(y)Ag_(1-y) (0.01≦y≦0.5) single-crystalline metal nanowire, a Ag₂Te nanowire and a Bi₁Te₁ single-crystalline metal nanobelt were prepared according to the method of the present invention (see Examples 1 to 4).

The following Example 1 is a representative example illustrating a method of fabricating a binary alloy nanowire without using a halide based precursor. Example 2 describes a method for fabrication of a binary alloy nanowire using a halide based precursor, Example 3 describes a method for fabrication of a binary alloy nanowire using a binary alloy substances used to form the binary alloy nanowire, and Example 4 illustrates a method for fabrication of a binary alloy nanobelt using binary alloy substances used to form the binary alloy nanobelt, respectively.

As described above, although Example 3 illustrates only the specific binary alloy substance of Ag₂Te as the precursor, a combination of the binary alloy substance of Ag₂Te and Ag in a form of a metal element or a combination of the binary alloy substance of Ag₂Te and a specific metal oxide such as Ag₂O₃ can also be applied instead of Ag₂Te. Likewise, although only the binary alloy substance of Bi₁Te₁ is used in Example 4 as the precursor, it can be replaced by a combination of the binary alloy substance of Bi₁Te₁ and Bi in the form of a metal element or a combination of the binary alloy substance of Bi₁Te₁ and a metal oxide of Bi₂O₃.

EXAMPLE 1

A Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire was synthesized in a reaction furnace using a vapor phase transport method.

The reaction furnace is generally divided into front and rear parts and equipped with a heating element and a thermostat, independently. The reaction furnace has a built-in quartz tube with a diameter of 2.54 cm (1 in) and a length of 60 cm (23.6 in).

A boat type container made of high purity alumina material was located in the middle of the front part of the furnace, to which a mixture including 0.03 g of Au₂O₃ (Sigma-Aldrich, 334057) and 0.03 g of PdO (Sigma-Aldrich, 203971) was added as a precursor. A sapphire single-crystalline substrate (surface (0001)) was positioned in the middle of the rear part of the reaction furnace. Argon gas flow was introduced to the front part and exhausted out of the rear part of the reaction furnace. To the rear part of the furnace, a vacuum pump was fixed to maintain an internal pressure of the quartz tube at 5 torr. Ar gas flow rate was controlled to 150 sccm using MFC (mass flow controller).

While maintaining temperatures of the alumina boat containing the precursor in the front part and the silicon substrate in the rear part of the furnace at 1100° C. and 950° C., respectively, the heat treatment was conducted for 30 minutes to produce the Pd_(x)Au_(1-x) (0.0≦x≦0.99) single-crystalline metal nanowire as a final product.

EXAMPLE 2

A Co_(y)Ag_(1-y) (0.01≦y≦0.5) single-crystalline metal nanowire was synthesized in a reaction furnace using a vapor phase transport method.

The reaction furnace is generally divided into front and rear parts and equipped with a heating element and a thermostat, independently. The reaction furnace has a built-in quartz tube with a diameter of 2.54 cm (1 in) and a length of 60 cm (23.6 in).

Two boat type containers made of high purity alumina material were located in the middle of the front part of the furnace, in which 0.01 g of CoCl₂ (Sigma-Aldrich, 449776) and 0.3 g of Ag₂O (Sigma-Aldrich, 22163) were placed as precursors, respectively. A Si single-crystalline substrate (surface (100)) was positioned in the middle of the rear part of the reaction furnace. A melting pot made of alumina containing Au₂O₃ was placed in the middle of the front part of the reaction furnace.

Argon gas flow was introduced to the front part and exhausted out of the rear part of the reaction furnace. To the rear part of the furnace, a vacuum pump was fixed to maintain an internal pressure of the quartz tube at 15 torr. Ar gas flow rate was controlled to 500 sccm using MFC.

Temperature of the front part (located in the middle of the furnace) was controlled to 1000° C. to allow the melting pot containing Ag₂O being maintained at 1000° C., another melting pot containing CoCl₂ was placed at a distance of 4 cm (1.57 in) apart from the melting pot containing Ag₂O so that the CoCl₂ containing pot was maintained at 650° C.

Whiling maintaining temperature of the rear part of the furnace to 800° C., the heat treatment was conducted for 30 minutes to produce the Co_(y)Ag_(1-y) (0.01≦y≦0.5) single-crystalline metal nanowire as a final product. To more clearly understand, construction of the heat treatment process as well as the precursors described in Example 2 were shown in FIG. 1.

EXAMPLE 3

An Ag₂Te single-crystalline metal nanowire was synthesized in a reaction furnace using a vapor phase transport method.

The reaction furnace is generally divided into front and rear parts and equipped with a heating element and a thermostat, independently. The reaction furnace has a built-in quartz tube with a diameter of 2.54 cm (1 in) and a length of 60 cm (23.6 in).

A boat type container made of high purity alumina material was located in the middle of the front part of the reaction furnace, in which 0.05 g of Ag₂Te (Sigma-Aldrich, 400645) was placed as a precursor. A Si single-crystalline substrate (surface (100)) was positioned in the middle of the rear part of the reaction furnace.

Ar gas flow was introduced to the front part and exhausted out of the rear part of the reaction furnace. To the rear part of the furnace, a vacuum pump was fixed to maintain an internal pressure of the quartz tube at 10 torr. Ar gas flow rate was controlled to 200 sccm using MFC.

While maintaining temperatures of the alumina boat containing the precursor in the front part and the silicon substrate in the rear part of the furnace at 1000° C. and 800° C., respectively, the heat treatment was conducted for 30 minutes to produce the Ag₂Te single-crystalline metal nanowire as a final product.

EXAMPLE 4

A Bi₁Te₁ single-crystalline metal nanobelt was synthesized in a reaction furnace using a vapor phase transport method.

The reaction furnace is generally divided into front and rear parts and equipped with a heating element and a thermostat, independently. The reaction furnace has a built-in quartz tube with a diameter of 2.54 cm (1 in) and a length of 60 cm (23.6 in).

A boat type container made of high purity alumina material was located in the middle of the front part of the furnace, in which 0.05 g of Bi₂Te₃ (Alfa Aeasr, 44077) was placed as a precursor. A Si single-crystalline substrate (surface (100)) was positioned in the middle of the rear part of the reaction furnace.

Ar gas flow was introduced to the front part and exhausted out of the rear part of the reaction furnace. To the rear part of the furnace, a vacuum pump was fixed to maintain an internal pressure of the quartz tube at 10 torr. Ar gas flow rate was controlled to 200 sccm using MFC.

While maintaining temperatures of the alumina boat containing the precursor in the front part and the silicon substrate in the rear part of the furnace at 600° C. and 150° C., respectively, the heat treatment was conducted for 30 minutes to produce the Bi₁Te₁ single-crystalline metal nanobelt as a final product.

All of the resulting products, that is, the binary alloy single-crystalline metal nanowires in Examples 1 to 3 and the binary alloy single-crystalline metal nanobelt in Example 4 were subjected to an analysis to monitor quality, morphology, purity, etc. of the products.

FIG. 2 to FIG. 5 show results measured for the Pd_(x)Au_(1-x) (0.0≦x≦0.99) single-crystalline metal nanowire fabricated by Example 1.

More particularly, FIG. 2 is a SEM photograph illustrating a Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire formed on a sapphire single-crystalline substrate. As shown in FIG. 2, a number of nanowires with uniform dimensions, each of which has diameter ranging 50 to 150 nm and length of more than 30 um (preferably, 30 to 50 um), were fabricated independent of the sapphire single-crystalline substrate. The nanowires had a linearly extended form in the direction of a longitudinal axis, a plurality of nanowires were individually separable without being held together, and the longitudinal axis of the nanowires was substantially perpendicular to surface of the substrate.

FIG. 3 shows an XRD result for the Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire verifying that the nanowire had crystallinity, which was different from that obtained for each of the Pd metal element and Au metal element.

FIG. 4 shows a result monitored by EDS fixed to a TEM device for analysis of constitutional ingredients of the nanowire in Example 1. From the result, it was understood that the fabricated nanowire comprised only Pd and Ag except additional materials inevitably measured due to characteristics of a certain measuring instrument such as a grid. Further, EDS analysis results for a number of nanowires fabricated according to the present inventive method demonstrated that Pd_(x)Au_(1-x) nanowires were fabricated (wherein, 0.01≦x≦0.99).

FIG. 5 shows TEM analysis results for the Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire, in particular, FIG. 5( a) illustrates a dark field image of the nanowire; FIG. 5( b) is a high magnitude TEM photograph of the nanowire shown in FIG. 5( a); and FIG. 5( c) illustrates a SAED pattern of the nanowire shown in FIG. 5( a).

Referring to FIGS. 5( a) and 5(b), it was found that a number of nanowires with smooth surface and a uniform thickness were produced. FIG. 5( c) showed that the fabricated nanowire was a single-crystalline product having FCC (face centered cubic) structure and a specified orientation of [100] for grain growth.

From the results monitored in FIG. 2 to FIG. 5, it was clearly understood that the fabricated nanowire was a single-crystalline product with FCC structure, which contained a solid solution of Pd and Au, and exhibited high quality and excellent morphology.

FIG. 6 to FIG. 8 show results measured for the Co_(y)Ag_(1-y) (0.01≦y≦0.5) single-crystalline metal nanowire fabricated by Example 2.

More particularly, FIG. 6 is a SEM photograph illustrating a Co_(y)Ag_(1-y) (0.01≦y≦0.5) single-crystalline metal nanowire formed on a Si single-crystalline substrate. FIG. 6 showed that a plate as well as the nanowire were formed simultaneously. From the high magnitude SEM photograph inserted in the upper left part of FIG. 6, it was demonstrated that a number of nanowires with uniform dimensions, each of which has diameter ranging 200 to 300 nm and length of more than several um, were fabricated independent of the Si substrate. The nanowires had a linearly extended form in the direction of a longitudinal axis, and a plurality of nanowires were individually separable without being held together.

The XRD result in FIG. 7 demonstrated that the fabricated nanowire had an FCC structure, which was substantially the same as that of bulk Ag.

FIG. 8 illustrates a dark field image of a Co_(y)Ag_(1-y) (0.01≦y≦0.5) single-crystalline metal nanowire and, in particular, a SAED pattern of the nanowire being inserted in the lower left part of FIG. 8.

From the results monitored in FIG. 8, it was clearly understood that the fabricated nanowire was a single-crystalline product with FCC structure and a specified orientation of [011] for grain growth.

FIG. 9 shows results monitored by EDS fixed to a TEM device for analysis of constitutional ingredients of a nanowire, in particular, FIG. 9( a) is an Ag EDS mapping result of the nanowire; FIG. 9( b) is a Co EDS mapping result of the nanowire; FIG. 9( c) is an EDS result of a white blank square portion indicated on an upper part of the nanowire; and FIG. 9( d) is an EDS result of an alternative white blank square portion indicated on a lower part of the nanowire.

From the results shown in FIG. 9( a) to 9(d), it was found that the fabricated nanowire comprised only Co and Ag except additional materials inevitably measured due to characteristics of a certain measuring instrument such as a grid and, in addition, Co and Ag ingredients were homogeneously dispersed in the nanowire. Further, EDS analysis results for a number of nanowires fabricated according to the present inventive method demonstrated that Co_(y)Ag_(1-y) nanowires were fabricated (wherein, 0.01≦y≦0.5).

From the results monitored in FIG. 6 to FIG. 9, it was clearly understood that the fabricated nanowire was a single-crystalline product with FCC structure, which contained a solid solution of Co and Ag, and exhibited high quality and excellent morphology.

FIG. 10 to FIG. 13 show results measured for the Ag₂Te single-crystalline metal nanowire fabricated by Example 3.

More particularly, FIG. 10 is a SEM photograph illustrating a Ag₂Te single-crystalline metal nanowire formed on a sapphire single-crystalline substrate.

As shown in FIG. 10, it was demonstrated that a number of nanowires with uniform dimensions, each of which has diameter ranging 150 to 200 nm and length of more than several um, were fabricated independent of the sapphire single-crystalline substrate. The nanowires had a linearly extended form in the direction of a longitudinal axis, and a plurality of nanowires were individually separable without being held together.

The XRD result in FIG. 11 demonstrated that the fabricated Ag₂Te nanowire had an SM (Simple Monoclinic) structure, which was substantially the same as that of bulk Ag₂Te.

FIG. 12 shows TEM analysis results of a Ag₂Te nanowire, in particular, FIG. 12( a) illustrates a dark field image and SAED pattern of the nanowire; FIG. 12( b) is a HRTEM photograph of the nanowire shown in FIG. 12( a) and, in addition, FFT pattern inserted in an upper right part of FIG. 12( b).

Referring FIG. 12( a), it was found that a number of nanowires with smooth surface and a uniform thickness were obtained and each of the fabricated nanowires was a single-crystalline product having an SM structure and a specified orientation of [302] for grain growth.

As shown in the HRTEM photograph of FIG. 12( b), it can be clearly understood that the fabricated nanowire was a high quality single-crystalline product without defects and an interplanar (crystal) distance of the nanowire was 4.46 Å, which was substantially the same as that of bulk Ag₂Te (010).

From the result monitored by EDS fixed to a TEM device for analysis of constitutional ingredients of a nanowire as shown in FIG. 13, it was understood that the fabricated nanowire comprised only Ag and Te except additional materials inevitably measured due to characteristics of a certain measuring instrument such as a grid and, in addition, a relative ratio of Ag to Te was 2:1.

From the results monitored in FIG. 10 to FIG. 13, it can be clearly understood that the fabricated Ag₂Te nanowire was a single-crystalline product with an SM structure and a relative ratio of 2:1 for Ag to Te, and exhibited high quality and excellent morphology.

FIG. 14 shows TEM analysis results of a Bi₁Te₁ nanobelt, in particular, FIG. 14( a) illustrates a dark field image and SAED pattern of the nanobelt.

Referring FIG. 14( a), it was found that a nanobelt with smooth surface and a uniform thickness was obtained. Also, FIG. 14( b) is a HRTEM photograph of the nanobelt together with FFT pattern inserted in an upper right part thereof.

FIGS. 14( a) and (b) showed that the fabricated nanobelt was a single-crystalline product having a hexagonal structure and a specified orientation of [110] for grain growth.

FIG. 15 shows a result monitored by EDS fixed to a TEM device for analysis of constitutional ingredients of a nanobelt fabricated as described in Example 4 of the present invention.

FIG. 16 shows an XRD result of a nanobelt fabricated as described in Example 4 of the present invention.

While the present invention has been described with reference to the preferred embodiment, it will be understood by those skilled in the art that various modifications and variations may be made therein without departing from the scope of the present invention as defined by the appended claims. 

1. A method of fabricating a binary alloy single-crystalline metal nanostructure, comprising: using two substances selected from a first material to a third material separately or in a combination thereof as a precursor; and heat treating the precursor as well as a semiconductor or insulator single-crystalline substrate under inert atmosphere after placing the precursor on front part of a reaction furnace and the single-crystalline substrate on rear part of the reaction furnace to fabricate a binary alloy single-crystalline metal nanowire or nanobelt, wherein the binary alloy for the nanostructure includes the first material containing metal oxides, metal substances or metal halides of a metal used to form the binary alloy, a second material containing metal oxides, metal substances or metal halides of another metal used to form the binary alloy, and/or the third material containing any one of binary alloy substances for the binary alloy.
 2. The method according to claim 1, wherein the precursor includes a mixture of the first material and the second material, a mixture of the first material and the third material, or the third material alone.
 3. The method according to claim 1, wherein metal halides of the first material or the second material are selected from a group consisting of metal fluoride, metal chloride, metal bromide and metal iodide.
 4. The method according to claim 1, wherein the inert gas flow is introduced through the front part to the rear part of the furnace at 10 to 600 sccm.
 5. The method according to claim 1, wherein heat treatment is conducted under pressure ranging from 2 to 30 torr.
 6. The method according to claim 1, wherein the precursor is maintained at 500 to 1200° C. while the single-crystalline substrate is maintained at 700 to 1100° C.
 7. The method according to claim 1, wherein the precursor is maintained at 500 to 1200° C. while the single-crystalline substrate is maintained at 100 to 200° C.
 8. The method according to claim 1, wherein the precursor is a mixture containing metal halides of the first material as well as the second material, and metal halides of the first material and the second material are physically separate from each other and positioned at the front part of the reaction furnace.
 9. The method according to claim 1, wherein metal halides of the first material are maintained at 500 to 800° C. and the second material is maintained at 800 to 1200° C., while the single-crystalline substrate is maintained at 700 to 1100° C.
 10. The method according to claim 1, wherein metal oxides of the first material or the second material are selected from a group consisting of silver oxide, gold oxide, cobalt oxide, palladium oxide and tellurium oxide.
 11. The method according to claim 1, wherein metal substances of the first material or the second material are selected from a group consisting of silver, gold, cobalt, palladium and tellurium in terms of metal element.
 12. The method according to claim 1, wherein metal halides of the first material or the second material are selected from a group consisting of silver halide, gold halide, cobalt halide, palladium halide and tellurium halide.
 13. The method according to claim 1, wherein binary alloy substances of the third material include Pd and Au alloy, Co and Ag alloy, Ag and Te alloy, or Bi and Te alloy.
 14. The method according to claim 1, wherein the binary alloy single-crystalline metal nanowire formed on the single-crystalline substrate is selected from a Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire, a Co_(y)Ag_(1-y) (0.01≦x≦0.5) single-crystalline metal nanowire, a Ag₂Te single-crystalline metal nanowire and a Bi₁Te₁ single-crystalline metal nanobelt.
 15. A binary alloy nanostructure comprising a solid solution of single crystals of two metal elements or a compound of the single crystals, in which the metal elements are selected from metals and metalloids, wherein the structure is fabricated by using a precursor under a catalyst through a vapor phase synthesis method.
 16. The nanostructure according to claim 15, wherein the precursor includes two substances selected from a first material to a third material separately or in a combination thereof, and the binary alloy for the nanostructure includes the first material containing metal oxides, metal substances or metal halides of a metal used to form the binary alloy, a second material containing metal oxides, metal substances or metal halides of another metal used to form the binary alloy, or the third material containing any one of binary alloy substances for the binary alloy.
 17. The nanostructure according to claim 15, wherein the vapor phase synthesis method is heat treatment characterized in that the precursor is maintained at 500 to 1200° C. while a substrate for fabrication of a binary alloy single-crystalline metal nanowire is maintained at 700 to 1100° C., and an inert gas flow is introduced from the precursor to the substrate at 10 to 600 sccm under pressure ranging from 2 to 30 torr.
 18. The nanostructure according to claim 15, wherein the vapor phase synthesis method is heat treatment characterized in that the precursor is maintained at 500 to 1200° C. while a substrate for fabrication of a binary alloy single-crystalline metal nanobelt is maintained at 100 to 200° C., and an inert gas flow is introduced from the precursor to the substrate at 10 to 600 sccm under pressure ranging from 2 to 30 torr.
 19. The nanostructure according to claim 16, wherein the binary alloy nanowire is selected from a Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire, a Co_(y)Ag_(1-y) (0.01≦x≦0.5) single-crystalline metal nanowire, a Ag₂Te nanowire and a Bi₁Te₁ single-crystalline metal nanobelt.
 20. The nanostructure according to claim 19, wherein the Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire has a FCC (Face Centered Cubic) structure.
 21. The nanostructure according to claim 20, wherein the Pd_(x)Au_(1-x) (0.01≦x≦0.99) single-crystalline metal nanowire is in the form of a solid solution.
 22. The nanostructure according to claim 19, wherein the Co_(y)Ag_(1-y) (0.01≦x≦0.5) single-crystalline metal nanowire has a FCC (Face Centered Cubic) structure.
 23. The nanostructure according to claim 22, wherein the Co_(y)Ag_(1-y) (0.01≦x≦0.5) single-crystalline metal nanowire is in the form of a solid solution.
 24. The nanostructure according to claim 19, wherein the Ag₂Te single-crystalline metal nanowire has an SM (Simple Monoclinic) structure.
 25. The nanostructure according to claim 24, wherein the Ag₂Te single-crystalline metal nanowire is in the form of a compound.
 26. The nanostructure according to claim 19, wherein the Bi₁Te₁ single-crystalline metal nanobelt has a hexagonal structure. 